Method and apparatus for screen printing fixed and variable indicia

ABSTRACT

Method and apparatus for printing a design along with selectable indicia such as code and date images upon the surface of a container by a single stencil screen assembly. A frame supports a principal stencil screen delineating the design for printing and a blank area. A relatively small auxiliary stencil screen delineating the indicia encloses the blank area by a sealed contact with the principal stencil screen so that ink or other types of printing media pass through both the blank area and the auxiliary stencil screen. In this manner, a stencil screen assembly can be made up as needed to meet the ever-changing needs to label containers of perishable items and mark the containers with shelf-life codes or dates.

United States Patent 1191 Miller July 15, 1975 METHOD AND APPARATUS FOR SCREEN PRINTING FIXED AND VARIABLE INDICIA [75] Inventor: Henry L. Miller, Mars, Pa.

[73] Assignee: Miller Screen & Design, Inc., Mars,

[22] Filed: Dec. 10, 1973 [2]] Appl. No.: 423,209

[58] Field of Search..... 10l/127, 129, 127.1, 128.1, 10l/128.2,l28.3,128.4,114,125,48-51, 112

Primary Examiner-Edgar S. Burr Assistant ExaminerR. E. Suter Attorney, Agent, or Firm-Brown, Murray, Flick & Peckham [5 7] ABSTRACT Method and apparatus for printing a design along with selectable indicia such as code and date images upon the surface of a container by a single stencil screen assembly. A frame supports a principal stencil screen delineating the design for printing and a blank area. A relatively small auxiliary stencil screen delineating the indicia encloses the blank area by a sealed contact with the principal stencil screen so that ink or other types of printing media pass through both the blank 1 References Cited area and the auxiliary stencil screen. In this manner, a UNITED STATES PATENTS stencil screen assembly can be made up as needed to 2,218,451 10/1940 Heyne 101/127.1 x meet the ever-changing needs to label containers of 2,730,038 l/1956 Goodbar et a1.... 101/112 X perishable items and mark the containers with shelf- 2,824,736 2/1958 Allen 101/112 X life codes or dates.

2,943,562 7/1960 Phillips et al. 101/112 X 3,800,697 4/1974 Sullivan 101/128.1 10 Clam, 4 D'awmg F'gures /6 PM =5I=============fi==::::::

I /4 1 2/ 1e Y 0 1t 0 @UR 50 AHRY [EUR 32 AHRY METHOD AND APPARATUS FOR SCREEN PRINTING FIXED AND VARIABLE INDICIA BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for printing, and more particularly, to a method and apparatus for printing in a single operation a design and preselected indicia upon the surface of an article wherein different indicia is selected from time-to-time for use with the same design.

Stencil screens are extensively employed to print designs upon the surface of mass-produced and unmarked containers. The term designs, as used herein, is intended to include decorations, the name of the packaged product and even more extensive information such as the name of a distributor or packager, a plant location or address and similar types of information. Typically, printing upon unmarked containers is performed immediately prior to the filling of the containers within a given processing line, although it may be carried out at other times with regard to the operations of a given processing plant. Most, if not all, packaged consumer products such as diary products, for example, are subject to at least local requirements that specify the need to apply daily or periodic markings that reflect the limited shelf-life of the product.

In the past, code or date information has been applied as a separate printing or stamping operation apart from the printing of the design on the mass-produced containers. This practice undoubtedly stems from the fact that it was not technically and economically feasible to incorporate code or date information along with the design in a single stencil screen assembly because it is impossible to predict the number of stencil screen assemblies that will be required since some of them may be prematurely damaged and therefore unusable.

More specifically, stencil screens are extensively used to print designs upon the rounded surface and tapered shoulder surface of molded plastic bottles used as containers for milk, fruit juices and the like. During printing, the screen may be moved along a straight-line path while the bottle is rotated about its axis in rolling contact with the screen. A printing medium, such as ink or a thermosetting material, is forced by means of a squeegee through exposed areas of the screen delineating the design for transfer onto the surfact of the bottle. Since typical printing of such bottles involves applying the design to opposed sides of the bottles, the screen must necessarily contact a mold seam which is a band of residual plastic in the bottle. This mold seam is an outwardly protruding excess of plastic material which results from the bottle molding process wherein excess plastic material flows into a very narrow gap at the parting line between mold halves. The mold seam, whether treated or not, acts as a knife-edge when contacting the moving stencil screen. The same area of the screen is repeatedly contacted by the mold seam and this stretches the screen and even severs the screen material. To some extent, the useful life of the stencil screen can be predicted on the basis of past experience. However, there are instances where, for example, a newly-installed stencil screen will be destroyed at the first printing of a bottle because it has an unusually sharp protrusion at one of its mold seams. Therefore, in the past it was not feasible to maintain a prepared supply of stencil screens to print designs along with the ever-changing date or code information.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for printing a design along with preselected indicia such as code and date images upon the surface of an article by a stencil screen.

It is a further object of the present invention to provide a method and apparatus for printing with a stencil screen wherein the stencil screen is photographically processed to define a desired image in a manner such that at a later time prior to actual use of the screen for printing, preselected indicia is added in an arbitrary way to the image defined on the screen.

It is still another object of the present invention to provide a method and apparatus for printing with a stencil screen that defines a design and a blank area for the passage of a printing medium from one side of the screen while supported in a frame to the other side of the screen and wherein the blank area is enclosed at the ink-transfer side of the screen by a preselected auxiliary stencil screen defining desired indicia for printing on an article during printing of the design.

It is a still further object of the present invention to provide a method and apparatus to reinforce an area of a stencil screen which is brought into repeated contact with the surface of an article so as to extend the useful life of the stencil screen and at the same time provide a method for printing preselected indicia at select times such as code and date images.

More specifically, the method according to the present invention for printing a design includes the steps of selecting a stencil screen defining a design and a blank area for the passage of a printing medium from one side of the screen while supported by a frame to the other side of the screen for transfer to an article, selecting an auxiliary stencil screen defining desired indicia for printing upon the article, enclosing the blank area by attaching the selected auxiliary screen to the stencil screen, and causing a printing medium to pass through the exposed spaces in the stencil screen forming the design and through exposed spaces in the auxiliary screen forming the indicia for deposit upon the surface of the article during a given printing operation.

The apparatus according to the present invention provides a stencil screen assembly comprising a frame having side walls defining an opening in the frame, a

- stencil screen larger in size than the opening, means for securing the stencil screen to the side walls in an overlying relation with the opening, an auxiliary stencil screen, means for securing the auxiliary stencil screen to the stencil screen and means for defining desired stencil patterns in both stencil screens.

These features and advantages of the present invention as well as others will be more apparent when the following description is read in light of the accompanying drawings, in which:

FIG. 1 is a plan view of a stencil screen assembly embodying the features for carrying out the novel method and apparatus of the present invention;

FIG. 2 is an enlarged partial side view of the stencil screen shown in FIG. 1;

FIG. 3 is a sectional view taken along line III-III of FIG. 1; and

FIG. 4 is a partial IVIV of FIG. 2.

According to the method of the present invention, the printing of a design is accompanied as an adjunct bottom view taken along line 3 to the printing operation by the printing of preselected indicia such as code and date images upon the surface of an article as, for example, a container for merchandise. The printing is performed by a stencil screen sometimes referred to in the art as a silk screen. The stencil screen is a unitary assembly and will be described in greater detail hereinafter. The stencil screen assembly which is ultimately employed for the printing process is actually a composite of two separate screens which have been previously processed to define desired images and then one screen superimposed upon the other whereby the printing process includes the stencil outline in both screens. It will be apparent to those skilled in the art that more than two stencil screens may by employed for a single printing process wherein two -or more auxiliary stencil screens are superimposed on a principal stencil screen which is supported directly by a frame. In this regard, such auxiliary stencil screens may be superimposed one on the other or the auxiliary stencil screens may be superimposed on the primary stencil screen at different areas.

With reference now to FIGS. 1 and 2, there is illustrated a stencil screen assembly which includes a rectangularly-shaped metal frame having opposed side walls 11 and opposed end walls 12. As best shown in FIG. 3, a molded rubber gasket 13 forms a contiguous member at the bottom of the walls 11 and 12 for supporting a main stencil screen 14. The screen 14 is stretched between the opposed walls under sufficient tension to avoid the development of undesirable ripples in the screen which would be detrimental to the printing process. The longitudinal sides of the screen are attached to an extended leg 15 of a U-shaped clamp 16 which is designed to fit tightly upon the upper edge of the side walls 11. Brackets 17 and 18 extend from the end walls 12. Each of these brackets has an opening into which there is received a rubber grommet 19. Passing through the grommet is a screw 21 having a nut 22 threaded on its upper end. The screws 21 are employed to hold metal compression clamps 23 at each side of the frame to the brackets 17 and 18, respectively, while electrically isolated therefrom. The metal compression clamp 23 is used as a transition member for clamping an end of the screen so that it can be, in turn, held under sufficient tension to the frame via the screw 21 and nut 22.

The screen 14 is processed using suitable well-known techniques for defining a desired design of an image to be printed. This is accomplished by impregnating the screen with an emulsion or other non-porous substance to leave a residual film 14A within the screen and to a limited extent at opposite sides of the screen. It will be understood that absence of the film 14A will expose the screen for the passage of a printing medium such as ink, paint and the like. In FIG. 1, for the purpose of illustration only, there are exposed areas of the screen forming the words Your Dairy" within an area of the screen. Following this is a blank area 34 wherein the screen is exposed by an absence of the film 14A. Following the blank area, there is a second area at 32 for the printing in the second instance of the words Your Dairy.

In the form illustrated in the drawings and according to the features of the present invention, an auxiliary stencil screen has the form of a rectangular piece of screen which has been processed using well-known techniques so that there is defined indicia such as code numbers or numbers representing a date by the absence of an emulsion or film in a similar manner as already described in regard to the main screen 14. The auxiliary screen 35 as shown in FIGS. 2, 3 and 4 defines indicia for printing the numbers 10, 3 and 41. It will be observed that these numbers are situated in the auxiliary screen such that they fall within the exposed screen area 34 of the main screen 14. The auxiliary screen 35 is made larger than the area 34 and the auxiliary screen 35 is positioned so that its edges overlie the film 14A defining the blank area 34 for sealing contact about the perimeter of the opening by means of glue, epoxy, heat seal, emulsion, sewing or other desired sealing methods. It is preferred, although not essential, to construct the rectangular shape of the auxiliary screen with a sufficient length so that end tabs extend up along the sides of the screen frame to the extent that they are separately attached to the U-shaped holding strips 16. In this manner, the auxiliary screen can be readily removed from the screen 14 and replaced as desired.

Thus, according to the present invention, the method of printing a design may be readily carried out by procuring a stored supply of screens bearing outlines of desired designs for printing. In the illustrative embodiment, this is generally represented by the words Your Dairy" twice repeated. In addition, a supply of auxiliary stencil screens containing different indicia such as numbers and/or' letters to form code or date images, can be prepared beforehand at relatively small procurement costs. When printing is to be undertaken, a selected stencil screen is made available and an auxiliary stencil screen containing the desired indicia is attached to it whereby the auxiliary stencil screen restricts and further confines the flow of printing medium through the area 34 to only the open areas in the auxiliary stencil screen. In the event the printing is to be car- .ried out through the use of a thermosetting ink, lead wires from a suitable power supply are attached to the screws 21 by means of additional nuts to jam against the nuts 22. In this manner, direct resistance heating of the screen 14 is brought about and a heating of the auxiliary screen 35 occurs by conduction. Ink is then deposited within the area defined by the frame and distributed across the face of the screen by the use of a squeegee or other well-known means. It is important to note that it is not technically feasible to form the blank area 34 by cutting the screen because this will increase the current intensity at this area cross the width of the screen and cause its destruction due to melting. Even when resistance heating of the screen is not to be effected, the removal of an area from the screen will cause the screen to from ripples and possibly distortions to the design which is to be printed.

As described hereinbefore, it is preferred to situate the auxiliary screen in relation to designs defined on the main screen so that the auxiliary screen will contact a seam area in a container when such articles and mode of printing are to be undertaken. In this manner, when contact printing is to be carried out, the auxiliary screen provides reinforcement for the main screen and thereby avoiding premature wearing and possible destruction of an otherwise usable screen assembly.

It is preferred to select a principal stencil screen with a mesh size which is larger than the mesh size used to form the auxiliary screen. Thus, for example, the principal auxiliary screen can be made out of screen material with a 200 mesh size while the auxiliary screen can be made out of screen material with a 230 mesh size.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

1 claim as my invention:

1. A method of printing a design along with preselected indicia such as an image corresponding to a code and/or a date upon the surface of an article by a stencil screen, said method including the steps of:

selecting a stencil screen defining a design and a blank area for the passage of a printing medium from one side of the screen while supported by a frame to the other side of the screen for transfer to said article;

selecting an auxiliary stencil screen defining desired indicia for printing upon the surface of said article; enclosing said blank area at one side of said stencil screen by releaseably attaching the selected auxiliary stencil screen thereto whereby, desired indicia on said selected auxiliary stencil screen can be changed without changing said stencil screen; and causing a printing medium to pass through exposed spaces in the stencil screen and through exposed spaces in the auxiliary stencil screen for transfer of the printing medium onto a surface of said article.

2. The method according to claim 1 wherein the selected auxiliary stencil screen is attached to the selected stencil screen after the latter is supported by said frame.

3. The method according to claim 2 wherein a portion of the selected auxiliary stencil screen overlies the edges defining said blank area, said method further including the step of sealing said auxiliary stencil screen to said stencil screen exclusive of said blank area.

4. The method according to claim 3 wherein said printing medium passes first through exposed spaces of said stencil screen and then through exposed spaces of said auxiliary stencil screen for transfer onto a surface of said article.

5. The method according to claim 4 wherein said step of selecting a stencil screen includes selecting an electrically-conductive metal stencil screen, said method including the further step of passing an electric current through the selected metal stencil screen for resistive heating thereof and conductive heating of the auxiliary stencil screen to heat a thermosetting printing medium for said step of causing a printing medium to pass through exposed spaces.

6. The method according to claim 5 wherein said step of selecting a stencil screen includes selecting a screen having a mesh size defining flow spaces for said printing medium which spaces are larger than the corresponding flow spaces in the sealed auxiliary stencil screen.

7. A stencil screen assembly comprising, in combination:

a frame having side walls defining an opening in said frame:

a stencil screen extending between the side walls of said frame;

means supported by said frame for securing said stencil screen to said side walls in overlying relation with said opening;

an auxiliary stencil screen;

means for releasably securing said auxiliary stencil screen in a superimposed relation upon said stencil screen at one side thereof, whereby, said auxiliary stencil screen can be changed without changing said stencil screen;

means for defining desired stencil patterns in portions of both of said screens overlying said opening; and

said means for securing said auxiliary stencil screen forming a seal. impervious to a printing medium, between the edge portions of said auxiliary stencil screen and said means for defining desired stencil patterns in said stencil screen.

8. A stencil screen assembly according to claim 7 wherein said side walls are pairs of opposed side members defining a rectangularly-shaped opening.

9. A stencil screen assembly according to claim 7 wherein said auxiliary stencil screen includes end tabs for attachment to said stencil screen at opposed sides of said frame.

10. A stencil screen assembly according to claim 8 further comprising means supported by said frame and connected to said stencil screen at opposed side walls of said frame for conducting an electric current through said stencil screen. 

1. A method of printing a design along with preselected indicia such as an image corresponding to a code and/or a date upon the surface of an article by a stencil screen, sAid method including the steps of: selecting a stencil screen defining a design and a blank area for the passage of a printing medium from one side of the screen while supported by a frame to the other side of the screen for transfer to said article; selecting an auxiliary stencil screen defining desired indicia for printing upon the surface of said article; enclosing said blank area at one side of said stencil screen by releaseably attaching the selected auxiliary stencil screen thereto whereby, desired indicia on said selected auxiliary stencil screen can be changed without changing said stencil screen; and causing a printing medium to pass through exposed spaces in the stencil screen and through exposed spaces in the auxiliary stencil screen for transfer of the printing medium onto a surface of said article.
 2. The method according to claim 1 wherein the selected auxiliary stencil screen is attached to the selected stencil screen after the latter is supported by said frame.
 3. The method according to claim 2 wherein a portion of the selected auxiliary stencil screen overlies the edges defining said blank area, said method further including the step of sealing said auxiliary stencil screen to said stencil screen exclusive of said blank area.
 4. The method according to claim 3 wherein said printing medium passes first through exposed spaces of said stencil screen and then through exposed spaces of said auxiliary stencil screen for transfer onto a surface of said article.
 5. The method according to claim 4 wherein said step of selecting a stencil screen includes selecting an electrically-conductive metal stencil screen, said method including the further step of passing an electric current through the selected metal stencil screen for resistive heating thereof and conductive heating of the auxiliary stencil screen to heat a thermosetting printing medium for said step of causing a printing medium to pass through exposed spaces.
 6. The method according to claim 5 wherein said step of selecting a stencil screen includes selecting a screen having a mesh size defining flow spaces for said printing medium which spaces are larger than the corresponding flow spaces in the sealed auxiliary stencil screen.
 7. A stencil screen assembly comprising, in combination: a frame having side walls defining an opening in said frame: a stencil screen extending between the side walls of said frame; means supported by said frame for securing said stencil screen to said side walls in overlying relation with said opening; an auxiliary stencil screen; means for releasably securing said auxiliary stencil screen in a superimposed relation upon said stencil screen at one side thereof, whereby, said auxiliary stencil screen can be changed without changing said stencil screen; means for defining desired stencil patterns in portions of both of said screens overlying said opening; and said means for securing said auxiliary stencil screen forming a seal, impervious to a printing medium, between the edge portions of said auxiliary stencil screen and said means for defining desired stencil patterns in said stencil screen.
 8. A stencil screen assembly according to claim 7 wherein said side walls are pairs of opposed side members defining a rectangularly-shaped opening.
 9. A stencil screen assembly according to claim 7 wherein said auxiliary stencil screen includes end tabs for attachment to said stencil screen at opposed sides of said frame.
 10. A stencil screen assembly according to claim 8 further comprising means supported by said frame and connected to said stencil screen at opposed side walls of said frame for conducting an electric current through said stencil screen. 